Printed circuit surge relief gap



Aug.

w. H. IBEAUBIEN PRINTED CIRCUIT SURGE RELIEF GAP Filed March 25, 1954 Fig.

Phoh cell conirol Fig. 3

lnvenfor 2 William' H. Beaubien His AHorney United States Patent Ofilice 2,901,659 Patented Aug. 25, 1959 PRINTED CIRCUIT SURGE RELIEF GAP William H. Beanbien, Beverly, Mass., assignor to General Electric Company, a corporation of New York Application March 25, 1954, Serial No. 418,718

12 Claims. (Cl. 313-309) My invention relates to electric surge relief gaps and more particularly to a printed circuit surge relief gap of improved construction.

Surge relief gaps are associated with or from a part of various electric circuits and devices to protect them from damage when surges of voltage resulting from electrical storms, switching operations or other disturbances are applied thereto through conductors which form a part thereof. Such gaps must break down at a predetermined voltage to discharge the surge voltage to ground and thereafter interrupt any flow of power current resulting from the discharge so that the circuit to ground is interrupted and the circuit or device to be protected is again insulated from ground for normal operation in accordance with its intended purpose.

It is an object of my invention to provide a surge relief gap apparatus having electrodes formed of metallic films bonded to an electrically insulated support and providing one or more are discharge paths.

It is a further object of my invention to provide a printed circuit surge relief gap which may form an integral part of a printed circuit panel.

It is also an object of my invention to provide a surge relief gap apparatus in which the electrodes are bonded to an insulating base which when subjected to are discharges produces arc extinguishing gases and conditions itself for subsequent discharges after the electrodes have been partially destroyed by said discharges.

It is also an object of my invention to provide a printed circuit surge relief gap in which the electrodes thereof are separated from one another by an aperture which extends through the electrode support and provides laterally of the electrodes an extended leakage path so that the width of the aperture determines the breakdown voltage of the gap.

Further objects of my invention will appear from the following descriptions thereof.

In carrying out my invention, in one form I provide an electric control device having a printed circuit which is applied to a phenolic impregnated paper base and inoludes electrodes each of which is provided with a plurality of definite points positioned opposite one another and extending to the edges of opposite sides of an elongated slot of substantially uniform width constituting the central portion of an aperture extending through said base and having end portions enlarged to provide extended electric current leakage paths at each end of said slot portion of said aperture.

My invention will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing in which Fig. 1 is a perspective view of the panel assembly of a street-lighting photoelectric controller embodying my surge relief gap, Fig. 2. is a plan view of the printed circuit panel forming part of the controller of Fig. 1 and including the surge relief gap of my invention, and Fig. '3 is a circuit diagram illustrating the location and connection in the controller circuit of the surge relief gap forming the subject matter hereof.

The assembly shown in Fig. 1 includes a panel 1 which mounts on its front side the component parts of a printed circuit including electrodes 2 and 3 of my surge relief gap. Also mounted on this panel and connected with certain printed circuit components thereof are clusters of contact clips which form sockets for a phototube 4 and two vacuum tubes 5 and 6 forming part of a photocell control circuit. These socket contact clips and their mounting on a printed circuit panel are described in and form the subject matter of an application Serial No. 264,669 of Charles N. Weiler filed December 29, 1951, which is now US. Patent No. 2,741,751 granted April 10, 1956, and assigned to the assignee of this invention.

Mounted on the back side of panel 1 and only partly shown in Fig. 1 are a plurality of electrical components such as miscellaneous resistors and capacitors, the above mentioned socket contact clips, a potentiometer, a fuse, a relay, a transformer and three contact prongs 7, 8 and 9, all of which are interconnected by their own terminals and the printed circuit components of panel 1 to form a photocell control which operates automatically to connect and disconnect one or more lamps to and from a source of supply in accordance with the light level as sensed by the photocell 4.

The panel assembly shown in Fig. 1 forms part of a plug-in unit of the type shown in US. Letters Patent 2,489,076, Arthur M. Bjontegard, granted November 22, 1949. The back portion of the assembly shown in Fig. 1 is enclosed by a cup of insulating material through which prongs 7, 8 and 9 extend and its front side is covered, except for the tubes thereof, by a metal cap which is grounded to the printed circuit component connected with prong 8.

The circuit arrangement, insofar as it is pertinent to my present invention, is shown in simplified form in Fig. 3 of the drawing. As shown in this diagram, prongs 7, 8 and 9 of the panel assembly are adapted for a plug-in connection with clips 7', 8' and 9' of a socket therefor. Clip 8' is connected to ground, to one side of a source of supply 10, and to one side of the lamp load 11. The other side of the source of supply is connected to socket clip 7 and the other side of the lamp load is connected to socket clip 9. When prongs 7, 8 and 9 are respectively connected with socket clips 7 8' and 9', lamp load 11 is connected tov the source of supply 10 through a fuse 12 and the contacts of a relay 13 provided these contacts are closed. Relay 13 is controlled by a circuit withinthe box identified as a photocell contro which is supplied with power through conductors connected with prongs 7 and 8. The electrodes 2 and 3 of my surge gap are connected between prongs 7 and 8 and are consequently across the supply conductors to the control circuit.

The printed circuit panel board 1 of Fig. 1 is shown in Fig. 2. Insofar as the circuits shown in Fig. 3 are concerned, it will be noted that the printed circuit components 2 and 3 thereof constitute the electrodes of my surge relief gap. In the assembly, printed circuit com ponent 3 is connected to prong 8 at hole 14 and printed circuit component 2 is connectedat holes 15 to a fuse clip paired with another fuse clip connected at holes 16 of printed circuit component 17 which is connected with prong 7 at hole 18. Also-printed circuit component 19 is connected at hole 20 to prong 9 and at hole 21 to one contact of relay 13 whose other contact is connected at hole 22 to printed circuit component 2. The assembly of parts, including others not noted above, is made on the panel board and its printed surface is then fluxed and dip-soldered by immersing the printed circuit surfacethereof in a bath of molten solder which unites the various parts and forms a strong physical assembly having good electrical conductivity between the printed circuit components and each of the parts making contact therewith. The circuit is then completed by inserting tubes 4, 5 and 6 to provide the operative device shown in fig. 1.

p The printed circuit panel board 1 may be fabricated in any suitable manner. Circuits are defined as printed when metallic films are produced on an insulating surface by any suitable process. These films may be produced by application of a desired metal through a stencil which determines the circuit pattern or by etching away the unwanted portions of a metallic foil which is initially applied over the whole surface of the panel and secured thereto by a suitable adhesive or bonding agent. In the etched foil process, a suitable resist is applied to the desired circuit portions of the sheet of foil which is bonded to its base or support and the undesired portions are then etched away by immersion in a suitable solvent. The resist patterns may be obtained by photographic methods, by offset printing or by applying paint through a nega tive silk screen stencil. I have employed panels produced by the photographic and silk screen methods.

In accordance with the preferred embodiment of my invention, I employ panels of laminated phenolic base material to which electro copper sheet foil is attached by thermosetting or thermoplastic tape. After the printed circuit has been formed as described above, the panel is then punched to produce the various mounting holes therein. It will be noted that my surge relief gap comprises elongated electrodes having a plurality of juxtaposed points separated from one another by an elongated aperture each end of which terminates in a hole of large size to provide laterally of the electrodes an extended leakage path so that the width of the aperture between the electrode points defines the breakdown voltage at each of these points. I prefer to form the elongated gap, which extends through the panel board and between the points of the electrodes of the surge gap, by means of sawing or cutting with a disc wheel. This gap should be substantially uniform in width and for establishing a breakdown voltage of 1200 volts, I form the elongated gap to have a width of .015 inch.

I have employed for the panel board a laminated phenolic paper base material satisfying the requirements of NEMA paper base grade XXXP which is suitable for the hot punching operation employed in forming the holes therein above referred to and described. This material has a high insulation resistance and low dielectric losses under severe humidity conditions. It is formed of cellulose paper which is impregnated and coated with a thermosetting resin binder and then consolidated under high temperature and pressure into a hard solid sheet product of high mechanical strength. The foil applied thereon and employed as circuit components is .0027 inch thick and the overall thickness of the printed circuit panel is .0625 inch. The foil is bonded to the panel board so as to resist a peeling force of six pounds applied to a one-inch strip of the foil. Furthermore, the foil must be bonded to the panel board so that it will not blister when subjected to a temperature of 235 centigrade for ten seconds. As previously stated, the assembly is completed by a dip-soldering operation and I have found that a 60 tin 40 lead solder is quite suitable, This solder melts at 450 to 470 Fahrenheit and secures the desired solder connection within about five seconds. The finished surge gap of my invention consequently is also coated with a thin film of this solder.

The etched foil clad laminate which I employ is particularly suited for acting as a component part of a surge relief gap since with each surge discharged across its electrodes, one or more of the cooperating points thereof are burned back and destroyed with the concurrent charring of the laminate which when subjected to the are produces arc quenching gases and conditions itself for subsequent discharges after all the salient points initially provided between the electrodes have been destroyed by the current surges discharged across the gap between these electrodes. Thus, while in the arrangement illustrated, eight pairs of points have been shown and it would consequently be believed that only eight discharges would be accommodated, experience has shown that the surge relief gap will continue to operate for its intended purpose after twenty or more discharges, the additional discharges being accommodated solely by the charred laminate at the gap between the burntback electrodes of the surge relief device.

It will be noted that in accordance with the construction I employ, each of the electrodes terminate at an edge of opposite sides of an elongated slot of substantially uniform width which forms part of an aperture which extends through the electrode support and has at each end of the slot portion an elongated end portion which provides an extended leakage path between opposite sides of the slot portion. These enlarged end portions of the aperture provide a peripheral portion, part of which is spaced beyond the striking distance of an are which is initiated between the electrodes and across the slot portion of the aperture. This construction prevents charting of the end portions of the slot or aperture which would give a leakage path laterally of the electrodes and consequently nullify the voltage characteristics established by the longitudinal slot portion of the aperture.

While I have noted above my preference for an etched foil clad laminate, it is of course apparent that films of metal produced in any suitable manner may be employed in place of foil and that the panel board need not of necessity be of the phenolic type in which the impregnating resin is essentially phenol-formaldehyde. Other laminated fibrous materials bonded by other types of resin or fiber board may be employed within the scope of my invention which contemplates the particular construction above described. Furthermore my printed circuit surge relief gap is not limited in its application to its location in a device of the particular type illustrated and described above in disclosing one form thereof.

In the circuit arrangement illustrated in Fig. 3, it will be noted that my surge relief gap is connected across the source of supply in circuit with a fuse 12. Such a construction is at times advantageous but is not a necessary arrangement when employing my invention since my surge gap will function for its intended purpose without having the added security of providing a fuse in circuit therewith. Thus, in accordance with another modification embodying my invention, the fuse 12 may be located in circuit with the contacts of relay 13 so that the electrodes of my surge gap are connected directly across the power input conductors of the device of which it forms a part. It is also apparent from what has been stated above that various means may be employed to form various printed circuits of which my surge gap forms a component part or that the surge gap may in itself constitute an independent element which may be associated with any suitable device. It is also apparent that my surge relief gap may be constructed to break down at any desired voltage in accordance with the physical gap provided between the electrodes and that a plurality of units such as disclosed above may be con nected in parallel or series or both to obtain desired operating characteristics.

Thus, while I have described, for purposes of illustration, a preferred embodiment of my invention, many modifications other than those suggested above will occur to those skilled in the art and I therefore wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claims as new and desire to secure by Letters Patent of the United States is:

1. Apparatus forming an electric surge relief gap and comprising two metallic conductor films each of which is bonded to an insulating base in juxtaposed position to the other and each of which respectively terminates at an edge of opposite sides of an elongated aperture extending through said base.

"2. Apparatus forming an electric surge relief gap comprising: two metallic films bonded to an electrically insulating support, said films constituting electrodes of a surge relief gap and respectively extending to the edges of opposite sides of an aperture which extends through said support and spaces them from one another by a predetermined distance.

3. Apparatus forrning an electric surge relief gap comprising: metallic foil bonded to a single surface of an insulating base and constituting a pair of electrodes which are spaced from one another by and extend to the opposite edges of an elongated aperture which extends through said base.

4. Apparatus forming an electric surge relief gap comprising: two metallic films bonded to an electrically insulating support, said films constituting electrodes each of which terminates at an edge of opposite sides of an elongated slot of substantially uniform width which forms part of an aperture which extends through said support, said aperture including at each end of Said slot an elongated end portion which provides an extended leakage path between opposite sides of said slot portion.

5. Apparatus forming an electric surge relief gap comprising: a pair of metallic foil electrodes bonded to a laminated phenolic impregnated paper base, each of said electrodes having a plurality of points which are directly opposite one another and terminate at an edge of opposite sides of an elongated slot of substantially uniform width forming part of an aperture which extends through said base, said aperture having at each end of said slot portion an enlarged end portion which provides an extended leakage path between opposite sides of said slot portion.

6. Apparatus forming an electric surge relief gap comprising: a pair of metallic foil electrodes bonded to an electrically insulating support, said electrodes respectively extending to the edges of opposite sides of an elongated slot portion of an aperture which extends through said support, said aperture having at each end of said slot portion an enlarged end portion which also extends through said support and has a periphery part of which is spaced beyond the striking distance of an arc which is initiated between said electrodes and across slot portion of said aperture.

7. Apparatus forming an electric surge relief gap, comprising: a printed circuit applied to an insulating panel, said circuit including a pair of electrodes which respectively extend to opposite edges of an aperture which extends through said panel and separates said electrodes.

8. Apparatus forming an electric surge relief gap comprising: a printed circuit applied to a phenolic impregnated paper base, said circuit including a pair of electrodes which are positioned opposite one another and extend to the edges of a slot of predetermined width formed in said base, said slot having at each end thereof an opening also formed in said base and providing an extended leakage path between opposite sides of said slot.

9. Apparatus forming an electric surge relief gap comprising: a printed circuit applied to a phenolic impregnated paper base including a pair of electrodes each of which is provided with a plurality of definite points positioned opposite one another and extending to the edges of opposite sides of an elongated slot of substantially uniform width which constitutes the central portion of an aperture which extends through said base, said aperture having end portions which are enlarged at each end of said slot portion to provide extended electric current leakage paths at each end of the slot.

10. Apparatus forming an electrical surge relief gap comprising: an insulating base formed of a material which chars when subjected to are temperatures and having an elongated aperture extending through said base, and two metallic conductor films bonded to said base, said films extending to an terminating at opposite edges of said aperture respectively.

11. Apparatus forming an electrical surge relief gap comprising: an insulating base formed of a material which chars when subjected to are temperatures and having an elongated aperture extending through said base, said aperture terminating in enlarged end portions providing extended leakage paths between opposite edges of said aperture; and two metallic conductor films bonded to said base, said films extending to and terminating at opposite edges -of said aperture respectively.

12. Apparatus forming an electrical surge relief gap comprising: an insulating base formed of a material which chars when subjected to arc temperatures and having an elongated aperture extending through said base forming a pair of opposed edges facing each other across said aperture, and two metallic conductor films constituting electrodes adhering to said base on one surface thereof, said films extending through and terminating at opposite edges of said aperture respectively.

References Cited in the file of this patent UNITED STATES PATENTS 330,486 Holt Nov. 17, 1885 945,293 Shinn Jan. 4, 1910 1,714,552 Everett May 28, 1929 2,131,717 Everett Sept. 27, 1938 2,263,752 Babler Nov. 25, 1941 2,555,971 Kolb June 5, 1951 2,758,074 Black et al. Aug. 7, 1956 2,795,725 Strab June 11, 1957 

